Basic principles of solenoid valves

Solenoid valves are used when it is necessary to control fluids automatically. These are increasingly used in the most varied types of plants and equipment. The variety of different designs that are available allows a valve to be selected specifically for each application in question.

Construction
Solenoid valves are control units, which when energized or de-energized, cut or allow the passage of a fluid. The actuator works with an electromechanical drive. When energy is applied, an armature pivots against the action of a spring, and when it disappears, the energy returns to its original position.

Valve operation
Depending on the mode of operation, it is possible to distinguish between valves piloted internally or externally. A distinctive feature is the number of connection ports or the number of paths or ways of flow ("ways").

Direct action valves
With a direct acting valve, the seat seal is fixed to the solenoid core. In de-energized condition, the seat hole is closed, which operates when the valve is energized.

2-way direct acting valves
The 2-way valves are valves that close with an inlet port and an outlet port. In de-energized condition, the core spring, assisted by fluid pressure, keeps the valve seat closed. When energized, the core and seat are opened by the action of the solenoid coil. The electromagnetic force is greater than the combined spring force and the dynamic and static pressure forces of the medium.

3-way direct acting valves
3-way valves have three port connections and two valve seats. One valve always remains open and the other closed in de-energized mode. When the coil is energized, the mode is reversed.

Solenoid valves internally piloted
With direct acting valves, static pressure forces increase when the diameter of the orifice does, which means that the pressure forces become correspondingly larger. Internally piloted solenoid valves are used to switch to higher pressures in conjunction with larger orifice sizes; in this case, the differential fluid pressure performs the main job by opening and closing the valve.

Internally piloted 2-way valves
The internally piloted solenoid valves are adjusted with 2 or 3 ways. A diaphragm or piston provides the seal for the main valve seat. When the pilot valve closes, the fluid pressure is transmitted to both sides of the diaphragm. The effective net pressure force from below now raises the diaphragm and opens the valve. In general, internally piloted valves require a minimum differential pressure to ensure satisfactory opening and closing.